Rossella Lau Lecture 1, DCO20105, Semester A, DCO Data structures and algorithms  Lecture 1: Introduction What this course is about:  Data structures & algorithms  ADT  Algorithm analysis  C++ -- By Rossella Lau

Rossella Lau Lecture 1, DCO20105, Semester A, What about data structures and algorithms  Structure: how data is organized  Place data contiguously  Place data here and there with “links”  Place data with “formula”  Algorithms: how to access data for a result  Scan data sequentially  Scan data according to the sequence of a structure  Scan data with “formula”  Algorithms: how to provide a smart solution

Rossella Lau Lecture 1, DCO20105, Semester A, Basic data structures  Basic data types a language supports:  Integer, float, double, char, boolean  string: usually an array of char supported with library  Data structures  A single datum in one of the basic types  A structure is a combination of the basic types A Product: code—string, description—string, price– double  A structure is a combination of basic types and structures A Sales: product—Product, quantity– integer

Rossella Lau Lecture 1, DCO20105, Semester A, Storage Container For storing multiple occurrences of a structure  Contiguous structures:  Array – supported by a language but needed care of array size, overflow  Vector – a structure to allow handling of its size and overflow “automatically”  Linked List: allow data connected by “links” to save space which may be wasted in an array/vector.  Combination of vector and linked list

Rossella Lau Lecture 1, DCO20105, Semester A,  reSize() “automatically” re-defines an array according to the structure defined in Vector.  There can be more: copy(), insert(), etc Algorithms A simplified view: clear process steps  E.g., A vector reSize(int newSize) { Define a new array with newSize if newSize >= capacity Copy the contents from *array to the new array Assign newSize to capacity Make the new array as *array Throw away the old array } class Vector{ int *array; int size; int capacity; …… };

Rossella Lau Lecture 1, DCO20105, Semester A, ADT An abstract model of a data structure together with the operations (can be treated as a form of algorithms) processed on the data structure.  In C++ or Java, an ADT can be implemented as a class.  Examples of the storage containers: vector and list (Text book slides: 1.4-8)

Rossella Lau Lecture 1, DCO20105, Semester A, Notes on the basic storage containers Vector and list allow data to be stored in different ways but not restricted to any order, or any operations, e.g.,  Data can be ordered in any sequence, even though searching may prefer a sorted one.  Operations support inserting an element in between elements of a vector, even though it may involve a lot of “shift” operations.

Rossella Lau Lecture 1, DCO20105, Semester A, Algorithms with “restrictive” containers When data in containers are organized with some kind of restriction, algorithms may be improved in many cases  E.g., sequential search and binary search ( Text book slides: )  Data can be stored in the basic storage containers in any order but they must be sorted before applying binary search

Rossella Lau Lecture 1, DCO20105, Semester A, Data structures in this course Many kinds of known containers allow “better” algorithms to be applied. In this course, we will look at some basic containers:  Vector, List, Deque  Map (Binary Search Tree)  Hash map  Stack and Queue

Rossella Lau Lecture 1, DCO20105, Semester A, Algorithm not related to a restrictive structure E.g., Linear search can find the maximum & minimun:  Can it be faster without sorting the container?  How about comparing max with the greater one of each pair in the container. int min = max = at(0).getValue; for (int i=1; i<siz(); i++) { if ( at(i).getValue > max ) max = getValue; if ( at(i).getValue < min ) min = getValu; } } // max and min is the result

Rossella Lau Lecture 1, DCO20105, Semester A, Algorithm at “low level” E.g., Use “cheaper” operations or better formula to achieve better execution time  int valueA / 2; can be rewritten as int valueA >> 1;  if ( value % 2 ) can be rewritten as if ( value & 1 )  We look for “smart” algorithms which may be or may not be related to a data structure

Rossella Lau Lecture 1, DCO20105, Semester A, Algorithm analysis To understand how good or how bad an algorithm is  Theoretically evaluate an algorithm  Execution time  Storage efficiency  Experimentally evaluate an algorithm  Use system clock to measure the execution time

Rossella Lau Lecture 1, DCO20105, Semester A, Algorithms in this course Other than basic algorithms related to the data structures in this course, in order to better algorithms and algorithm analysis, some sorting methods will be studied, e.g., :  Selection sort  Insertion sort  Merge sort  Quick sort

Rossella Lau Lecture 1, DCO20105, Semester A, C++  An O-O language for this course  Powerful, flexible  With a Standard Library and a Standard Template Library  Students can learn one more language in the programme  Major differences with Java  Not necessary to be a class inside a program  Using template much more than polymorphism  An object can be referenced in three forms: a real object, a pointer (including iterators), and a reference.

Rossella Lau Lecture 1, DCO20105, Semester A, Summary  This course studies basic data structures and algorithms with C++ implementation  Organization of a data structure may allow better algorithms to be applied  Algorithms can be smarter without a special organization of a data structure  There are ways to measure or evaluate an algorithm

Rossella Lau Lecture 1, DCO20105, Semester A, Reference  Ford: 1.2-3, 3.2  C++ Complete Reference  Lecture 1 of last year -- END --